Experts say the neogothic clock tower — one of the world’s most recognizable landmarks — is gently leaning to one side. Documents recently published by Britain’s Parliament show that the top of its gilded spire is nearly 18 inches out of line.

The 315-foot tower is leaning in the northwest direction at an angle of 0.26 degrees, according to a report from 2009.
But there’s no cause for alarm, experts said. It would take thousands of years before the London landmark’s tilt matches that of the Leaning Tower of Pisa.

The clock tower — colloquially known as Big Ben — has been slightly off center since it was erected in the mid-19th century. Like many old buildings, its position has been shifting due to environmental factors such as seasonal temperature and moisture level changes.

“We’re talking about unbelievably small movements,” said John Burland, an engineering professor at Imperial College London who has been involved in the study on the tower.

“At the present rate, it will be 10,000 years before we reach that,” he added.

Even so, the tilt might now be just about visible to the naked eye.

“Anyone who stands there and looks may say ‘I don’t think it’s vertical,’ and they are quite right,” he said.

Most of the tilt took place during the first years when the tower was being built, likely due to nonuniform ground conditions, Burland said.

Mike McCann, who’s charged with looking after the tower’s clockwork, shrugged off the problem, saying that such imperfections were a fact of life for older buildings.

“The Victorians didn’t have lasers or modern surveying equipment,” said McCann, whose official title is Keeper of the Great Clock. “It was never going to be straight to start with.”